Application of 31P and 27Al MAS NMR for phosphate speciation studies in soil and aluminium hydroxides: promises and constraints

Analysis of Aluminum Hydroxyphosphate Vaccine Adjuvants by 27Al MAS NMR

“…Lookman et al showed that tetrahedral aluminum can form from octahedral aluminum by drying samples at elevated temperatures and presumably driving off water ligands. 17 However, several of the samples from the present study were analyzed as wet slurries, i.e., without lyophilization, and the NMR spectra were not altered.…”

“…18 Nevertheless, tetrahedral aluminum is consistently observed in aluminum phosphate precipitates as seen here and in other studies. 7,9,10,17 Tetrahedral aluminum in these precipitates is clearly related to the presence of phosphate because it is not observed when phosphate is not present. The location of the tetrahedral peak by 27 Al MAS NMR correlated with the amount of phosphate present, though the relative magnitude of the peak correlated only weakly.…”

“…Lookman et al performed a similar experiment to study phosphate adsorption in soil. 17 After adding 3 mM phosphate to samples of amorphous aluminum hydroxide, they observed slight shoulders on the octahedral peaks indicating the formation of phosphate-containing aluminum hydroxyphosphate. The magnitude of the effect they observed was relatively quite small and may not be detectable with the current experiments.…”

Identification of inositol hexakisphosphate binding sites in soils by selective extraction and solution 31P NMR spectroscopy

“…The oxalate solution is used to extract amorphous Al and Fe oxides as well as P bound to those oxides, but does not extract more crystalline metals (García-Rodeja et al, 2007;Gleyzes et al, 2002;Jan et al, 2013;McKeague et al, 1971a;McKeague and Day, 1966). It also extracts amorphous Al and Fe associated with organic matter (McKeague et al, 1971b) and calcium-bound P due to pH dependent dissolution of Ca compounds (Lookman et al, 1997;Uusitalo and Tuhkanen, 2000), although the acidic pH in the soils used in this study suggests that Ca compounds are unimportant as sorption sites for P in these soils. The identification of IP 6 in oxalate extracts of soils by solution 31 P NMR spectroscopy is to our knowledge the first evidence for the chemical nature of P in oxalate extracts of soils and shows that oxalate extractable P can contain considerable concentrations of IP 6 .…”

Geochemical and mineralogical investigation of domestic archaeological soil features at the Tiel-Passewaaij site, The Netherlands

“…Also, well-crystallized Fe-P compounds have been reported to dominate P amended soils (Borggaard et al, 2005). An explanation for the non-crystalline Fe-P phases may be periodic dissolution of amorphous metal oxides due to, for example, changes in the water table and subsequent precipitation of P. An analogous mechanism has been suggested for enhanced retention of P by amorphous Al-oxides (Lookman et al, 1997). Borggaard et al (2005) additionally suggest that the affinity of amorphous Fe-oxides for P increases with time.…”